Paint comprises a film-forming continuous phase component that may be aqueous or non-aqueous, which contains a polymer as a solute or as a colloidal dispersion. This film-forming component is known as the binder and is the only component that is necessary to make a paint composition. Pigments are particulate compounds which can be dispersed in a medium, resin, or polymer binder to provide hiding power and to provide color to paints and coatings. Pigments may also improve the strength and adhesion of the paint film, improve the durability and weathering properties, provide opacity and special effects (e.g., flip, sparkle), and modify flow and application properties. Pigments can be divided into natural or synthetic, and organic or inorganic. Metallic/pearlescent pigments are used for decorative purposes to create luster effects in coatings. Pearlescent effects can be achieved by coating thin flakes with one or more layers of a metal oxide such as titanium dioxide or iron oxide. Light diffraction and interference occur in these layers produce a pearlescent effect. Metallic/pearlescent pigments are generally heavier than other pigments and are harder to disperse.
Pigments can be dispersed into paints in a dry powder form or in a colorant liquid composition. Colorants are not paints and comprise much less binders than paints. Colorants that can be used with either aqueous latex or solvent-based surface coatings are called universal colorants. Heavy pigment particles must be separated from one another and evenly distributed throughout colorant compositions as a colloidal suspension. Otherwise, a variety of defects can occur such as color shift, flooding and floating, settling and loss of gloss. Pigments that have no charges on them and are not coated need surfactants/dispersants for better distribution. Traditional formulations use volatile organic compounds (VOC) to control the effectiveness and suspension of pigments. For example, a wetting agent or surfactant, such as alkylphenol ethoxylate (APE), is used to improve the distribution of pigment particles. These wetting agents or surfactants are often volatile and generate odor.
Due to environmental concerns, among other things, there has been a movement toward reducing the amount of volatile organic compounds (VOC) in paints, stains, and other coating compositions. Various attempts have been carried out to produce low-VOC or zero-VOC colorants. U.S. Pat. No. 7,659,340 to Coward et al. discloses a low-VOC universal colorant composition including a colorant component, a surfactant package including at least one alkyd-compatible surfactant and at least one latex-compatible surfactant, and a carrier, wherein the surfactant package is substantially free of APE and wherein the colorant-to-binder ratio is from 0.5 to 14.3. US 2011/0092641 to Parris et al. discloses a method of preparing solventless universal colorants comprising milling a pigment in a resin that is soluble in both water and organic solvent, wherein the resin contains both hydrophobic and hydrophilic monomers.
There remains a need for developing a universal metallic/pearlescent colorant that contains no VOCs including APE and formaldehyde, and preferably no resin. Having a color palette with a metallic/pearlescent backbone that is tintable in both a pastel and deep color helps broaden the capability of color effects.